Stirrer for microwave ovens



April ,v 1970 R. FREELAND I 3,505,491

STIRRER FOR MICROWAVE OVENS ,FIGJ

Filed Jan. 24, 1968 2 Sheets-Sheet 1 INVENTOR ROYDEN R. FREELAND ATTORNEYS:

April 7, 0 v R. R. FREELAND f STIRRER FOR MICROWAVE OVENS 2 Sheets-Sheet 2 Filed Jan. 24, 1968 FIG. 5

ROYDEN R. FREELAND WJ/M ATTORNEYJI 3,505,491 STIRRER FOR MICROWAVE OVENS Royden R. Freeland, Morgan Road at Edmond Road, Oklahoma City, Okla. 73110 Filed Jan. 24, 1968, Ser. No. 700,059 Int. Cl. Hb 9/06 US. Cl. 219-1055 6 Claims ABSTRACT OF THE DISCLOSURE A stirrer for microwave ovens including a hub with a plurality of blades radiating therefrom. The blades are positioned on the hub with an air gap provided between the blades adjacent the hub. The air gap provides a discharge path when reflective voltages become too high.

The conventional stirrers used in microwave ovens consist of rods, plates or blades which are rotated or reciprocated in the oven cavity for the purpose of breaking up the field pattern. The prior microwave ovens contain a disadvantage in that there is no provision for a discharge path when reflected voltages in the oven cavity become too high resulting in arcing in the magnetron. This of course is very disadvantageous resulting in shortening of the life of the magnetron. The present invention contemplates a means whereby a discharge path is provided in the stirrer itself to thereby prevent arcing in the magnetron.

One of the problems in using microwave ovens for cooking is the critical loading factor of the oven, in that high reflected waves developed can cause the magnetron to are and thereby be damaged. The present invention provides a discharge path by having gaps between the blades at the hub of the stirrer. With gaps of the proper dimensions, the discharge level can be made such that the arcing will occur at the hub of the stirrer and not within the magnetron itself. This discharge serves not only to dissipate energy, but will warn the user that the oven is not properly loaded and operation should not be continued until the loading is adjusted.

It is therefore an object of the present invention to provide an improved stirrer for a magnetron operated microwave oven in which a discharge path is provided in the stirrer itself which will prevent arcing in the magnetron.

It is a further object of this invention to provide an improved stirrer for microwave ovens which may be readily and economically produced.

The means for accomplishing the foregoing objects and other advantages, which will be apparent to those skilled in the art, are set forth in the following specification and claims and are illustrated in the accompanying drawings dealing with a basic embodiment of the present invention. Reference is made now to the drawings in which:

FIG. 1 is a schematic side view of a microwave oven incorporating the inventive stirrer;

FIG. 2 is a partial top plan view of the inventive stirrer;

FIG. 3 is a plan view showing only that end of a single blade which is attached to the hub of the stirrer;

FIG. 4 is a perspective view of the hub portion of the stirrer without the blades being mounted thereon;

FIG. 5 is a partial section view taken along line 55 of FIG. 2; and

FIG. 6 is a bottom plan view of the stirrer.

Turning now to FIG. 1, a microwave oven 10 includes a cooking cavity 11 within the housing 12 with access to the cavity being provided through the door 13. A magnetron and power supply 14 are positioned within the housing and are adapted to feed microwaves through United States Patent wave guide 15 into the cooking cavity 11. A stirrer 16 is mounted in the top of the cavity and is rotated by a driving motor 17 to break up the standing wave pattern formed within the cooking cavity.

Turning now to the details of the inventive stirrer; in reference to FIGURES 2 to 6, the stirrer 16 includes a hub-18 with a plurality of blades 19 to 22 fixedly mounted thereon and extending radially therefrom. Of course the number of blades may be varied according to the desired uses.

FIGURE 4 shows the details of the hub 18, which in this instance is square to satisfy the requirement for four blades, with diagonal slots 23 formed in each of the peripheral faces thereof. FIGURE 3 shows the end of the blades 19 to be received within the grooves 23. Of course, all of the blades will be identical. However, for the sake of clarity, only blade 19 is referenced. Portion 24 is received in groove 23. Portions 25 and 26 engage the top and bottom surfaces respectively of the hub 18. Portion 27 engages with the bottom surface of the adjacent blade, for example considering blade 19, portion 27 would engage the bottom side of blade 22. The gap is formed by portion 28 and the top surface of the adjacent blade, again considering blade 19, the gap would be formed between portion 25 and the top side of blade 20.

The air gap formed between the blades can perhaps be best seen in FIG. 5 wherein the air gap between portion'28 of blade 19 and the top surface of blade 20 is shown.

The blades are fixedly mounted on the hub. In the drawings the blades are welded to each other along portion 27 and the underside of the adjacent blade, the gaps being on the side of the stirrer opposite the welds 29. The engagement of portions 24 to 26 with the hub 18 provide positive engagement so that the welds illustrated will give adequate strength to the stirrer.

As a specific example, blades 2" wide may be mounted on a hub square with portion 28 of the blade extending to provide an air gap .025" between the adjacent blades. It has also been found that a suitable angle for inclination of the blades is 30 from the horizontal with the overall length of the blade being 5 long. Such a blade is suitable for use in a microwave oven having a cooking chamber of approximately 11 in depth, 11%" in width and 8" high at the opening and a magnetron operating at a frequency of 2450 mHz. feeding microwaves to the chamber.

The present invention may be embodied in'other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore to be embraced herein.

I claim:

1. In a microwave oven having a magnetron, an improved stirrer comprising a hub, a plurality of blades fixedly mounted on said hub radially extending outwardly therefrom, said blades having such configuration as to define at least one open air gap between junctions of overlapping end portions of at least one pair of adjacent blades near their connection to said hub, the width of said gap being a function of desired voltage breakdown thereby providing a discharge path when reflected voltages of the standing waves in said oven become too high thus causing voltage breakdown to occur in the stirrer rather than in the magnetron.

2. An improved stirrer according to claim 1 wherein said air gaps are formed between an end portion of one blade and a surface of an adjacent blade.

3. An improved stirrer according to claim 1 wherein said air gaps are provided between each pair of adjacent blades.

4. An improved stirrer according to claim 1 wherein said hub is provided with a plurality of grooves in the peripheral surface thereof, one end of each of said blades being profiled to engage in said groove. 7

5. An improved stirrer according to claim 4 wherein said blade is further profiled to engage with top and bettom'surfaces of said hub.

6. An improved stirrer according to claim 4 wherein said blade is further profiled to engage with one surface of one adjacent blade on one side of said hub and to form said air gap with the other adjacent blade on the other side of said hub, said blades being fixed by welding along the engaging portions of said blades.

References Cited FOREIGN PATENTS 9/1964 France.

JOSEPH V. TRUHE, Primary Examiner L. H. BENDER, Assistant Examiner 

